JP2005037397A - Ultrasonic gas flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic gas flowmeter provided with an essentially improved output, by taking reduction and study of temperature stability and an original temperature shape into account. <P>SOLUTION: This ultrasonic gas flowmeter comprises a gas through-flow measuring tube provided with a transmission sound converter and a reception sound converter, and a transmission and reception evaluating electronic part. Sound converters 7, 8, 9, 10 are formed as capacitive electro-acoustic type ultrasonic converters to constitute a sensor provided with improved output ability, in particular, the reduction and the study of the temperature stability and the temperature shape, and a device is provided to comparison-regulate the gas temperature shape and to minimize an influence of the temperature shape in flow measurement. Accurate and sure detection for gas, in particular, a volume flow or a mass flow in a highly dynamic flow is attained for a method for detecting the gas through-flow to detect a gas flow detected by two acoustic signals between a transmitter having high time-serial resolution of an average flow velocity and the flowing gas in an operation time, and a receiver. An assumed value for a flow rate is thereby evaluated after determining the operation time (35), and the assumed value is corrected based on at least a characteristic temperature of the gas and a temperature of a wall of the measuring tube (36). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultrasonic gas flow meter including at least one transmission converter, one reception converter and one transmission, reception and evaluation electronics, an apparatus for measuring exhaust gas from an internal combustion engine, and a gas flow-through. Regarding the method of detection, in this case the average flow velocity and thereby the amount of gas flowing is ascertained by two sound signals between the transmitter and the receiver with a higher temporal resolution from the operating time.

  Such ultrasonic gas flowmeters are known for fluids and gases and are the subject of various books and specialty articles. Ultrasonic gas flowmeters use a so-called entrainment effect, that is, the propagation speed and direction of the sound signal of the fluid not only depends on the orientation of the sound transmitter and the sound speed of the (stationary) medium, but above all on the flow speed of the fluid medium. Also depends. If at least two operating times are measured along at least two measuring lanes (Messpfaden), at least one of them must be directed upstream or downstream in parallel or diagonally to the flow direction. The extensions for the other measurement lane are crossed and translated or converged in parallel.

  At least two operating times of the transmitted sound feature in the region of the flowing medium are determined from at least two measured time differences between the transmission time and reception time of the sound feature. From the operating time, an average flow rate can be determined, which gives a volumetric flow determined by a known cross-section of the tube through which it flows.

  The mass flow of the flowing gas can be calculated from the volumetric flow if the concentration of the gas is known. However, this is not generally known, especially with pulsating gas flows with overlapping pressure pulsations and strong temperature fluctuations. The effective propagation speed of the sound that approximates the sound speed of the stationary gas is determined from at least two operating times of the transmitted sound feature and at the same time the actual gas pressure and possibly additional realities to measure the operating time. It is possible to measure the gas temperature and take them into account in the evaluation.

  However, this known method has limited application possibilities at that time. This is because, according to known equations for ideal gases, for accurate measurement of gas mass flow, additional knowledge of the adiabatic coefficient of the gas, which is the relationship between a specific pressure and a specific heat capacity at a constant volume, or mole Knowledge of mass is necessary. These values are necessary. However, these values are not always known and are not constant over time, for example in exhaust gases from variably introduced combustion.

  Besides that, the value obtained from the average flow velocity and the operating time of the sound velocity depends on the temporal and steric course of the flow in the volume which is advanced by the sound waves. Each of these values is a value transmitted through the sound path and time, and the flow rate transmitted over the cross section of the tube is a criterion for measuring the amount of gas flowing between them. Since both these transmissions generally do not give the same result, an expensive system has been devised to minimize the effect of flow shape on the values transmitted from the velocity and speed of operation in the sound path. For example, it has been proposed to position a plurality of ultrasonic transducers such that the flow velocity detected from the operating time matches the velocity already transmitted across the tube cross section. In addition, special sound paths in the vicinity of the tube wall have been proposed, especially for large tube cross sections. Multiple sound transducers and sound paths are appropriate, but expensive arrangements and evaluations should ensure that the flow velocity detected from the operating time is already consistent with the velocity transmitted across the tube cross section. there were.

  Furthermore, it is known that error correction can be processed in the form of calibration constants to take into account the flow shape present in the medium, which is, of course, only valid for constant flow characteristics in time. However, it is not useful in non-stagnation and pulsating flows.

  A disadvantage of the known devices and methods is that they start from a straight path of the sound path in the tube, in particular where they are often mis-flowed.

  Moreover, as is well known, the directional flow in the measuring tube has a great influence on the sound path and the measurement result of the ultrasonic gas flowmeter. Therefore, for corrective measures against such swirl speeds, flow forming installations in the measuring tube are recommended, for example flow rectifiers or layer generators in the form of thin plates or thin tubes.

  However, in general, it is not considered that sound refraction occurs on the basis of the axial flow shape in addition to the drift that changes sound. Starting from a value of zero in the front pocket of the transducer that is mounted obliquely on the measuring tube and in the ultrasonic transducer diaphragm, the flow rate has a smooth spread to the maximum velocity at about the center of the tube and Due to the dependence of the local sound velocity, the flow velocity causes a local sound impedance spread and its gradient causes refraction.

  The additional refraction as a result of the temperature shape in the flowing gas, which is likewise not considered in the prior art, is particularly important. In particular, it can be a sound path that strongly deviates from the linear progression of sound waves in the temperature difference between the measuring tube and the medium.

  In extreme cases, the sound emitted from the transmitter during the alignment of the transmitter and receiver is so powerful that the sound is no longer mainly input to the receiver, so that the operating time can no longer be measured. It can occur that it is deflected and refracted. In this case, it can be observed, for example, in measuring the amount of exhaust gas from an internal combustion engine. In sudden load conversion from idling to full load, for example, the temperature difference between the flowing exhaust gas and the pipe is 300 ° C and high flow velocity, which forms extreme flow and temperature shape, deflecting the sound of linear propagation Depending on the tube dimensions, it is guided up to several centimeters.

  Sound drift and refraction in a non-stationary gas flow with a non-stationary temperature shape is measured by inputting a part depending on the instantaneous flow characteristics of the maximum detectable amplitude to the receiver. Furthermore, the sound transmission can be very distorted and attenuated by the local eddy currents and the pressure reduction to the cavitation effect. This severely weakening flow leads to a strong influence of the amplitude and signal shape of both received signals, which in turn leads to high requirements on the evaluation method, sound transducer and overall arrangement. This result clearly limits the available measurement range of the flow meter and makes data evaluation difficult. Furthermore, the installation of a flow meter in the engine test stand represents a difficult environment for sensor electronics with respect to EMV (electromagnetic compatibility). Conventional systems and evaluation methods, for example cross-correction with stored reference signals (European Patent Application Publication No. 0797105 “Patent Document 1”) or any threshold response method used (German Patent Application Publication No. 196336945). The specification “Patent Document 2”) cannot satisfy all these requirements.

  The flow velocity to be measured in the exhaust pipe can include a large range of values, especially when the normal standard diameter for the measuring pipe is to be used in the exhaust line, irrespective of the size of the engine. With regard to maximizing the measuring range, there are proposals with appropriate correction angles for the special mechanical alignment of the transducer (by KSMylvaganam, "Wide range ultrasonic gas flow meter for monitoring sudden gas", ultrasonic, ferroelectric) And IEEE processing in frequency control, 36, 144-149, 1989 “Non-Patent Document 1”). However, this requires higher finishing technical costs for the measuring tube and does not allow permanent application for different flow rates and different temperature shapes.

  The exhaust gas temperature can be a value from −40 ° C. (for example, when the engine starts cold in the air-conditioning room) to approximately 1000 ° C. in the exhaust gas train depending on the operating state of the internal combustion engine and the position of the flow meter. Current equipment (eg from Sick AG) is strongly limited to the maximum allowable exhaust gas temperature (200 ° C.), for example, due to the use of piezoceramic ultrasonic transducers.

  The fact that the exhaust gas temperature of the internal combustion engine can be changed quickly and powerfully by changing the load of the engine operation, for example, at the full load in the traction operation is important. Based on this large and rapid change in flow characteristics, unpredictable refraction and overlap of the original received signal with parasitic sound signals can occur, which has led to false results when using conventional evaluation methods.

  Known ultrasonic gas flowmeters have the difficulty of detecting pulsations present in the exhaust gas flow at a considerable degree of pressure and flow velocity with sufficient accuracy. Based on the scanning theorem, ie to avoid measurement facts (aliasing), the signal to be measured should be high so that the scanning frequency is at least twice as high as the frequency of the signal component present in the signal at high frequencies. It is necessary to scan at a frequency. Therefore, the exhaust gas flow meter must have a suitable and high measurement repetition rate. For example, for passenger car engines, start from a repetition frequency of at least 3 kilohertz, depending on the position of the mass flow meter in the exhaust gas train. Devices on the market (eg Sick AG) operate at a measurement repetition frequency of up to 30 Hertz.

  Based on the special conditions governing the exhaust pipe, the evaluation method used for the exhaust gas sensor further possesses the appropriate possibility of reliable control of the detected flow-through value.

  The fundamental improvement in gas ultrasonic flowmeters means the adoption of positive displacement ultrasonic transducers, which have already been proposed in general (IJO'Sullivian and WMDWright, “Electrostatic Conversion”). However, it is known that most of the above problems can be solved. Elsevier Ultrasonics, Vol. 40, pp. 407-411, 2002 “Non-Patent Document 2”) In particular, evaluation methods, converters and requirements suitable for the exhaust gas train of an internal combustion engine are not known in use.

  A common difficulty in an ultrasonic transmission / reception transducer for gas is to send sufficient sound energy to the medium and obtain a sufficiently strong electrical reception signal from the received sound energy. Conventionally, a practically exclusive piezoelectric ultrasonic transducer has been adopted as the transducer, which excels with a simple structure made of solid-state material. In so doing, the solid state has a special wave resistance approximately 100,000 times higher than that of the gas, so that the large difference in the acoustic resistance of the gas medium on the one hand and the sound conversion material on the other hand becomes an obstacle. That means that most of the sound energy at the critical surface is reflected from the transducer to the gas medium and propagates only a small percentage. Therefore, in the large frequency range, this transducer has very little sensitivity and transmits and receives.

  The same characteristics have the result that piezoelectric sound transducers are much better than solid-state acoustic resonances with characteristic natural frequencies, or relatively high vibration quality with narrow band-like frequency characteristics. This fact is achieved and used to achieve a sufficiently high sensitivity: this narrow band-like frequency range results in an acceptable high sensitivity in the range of its natural or resonant frequency, i.e. on the basis of resonance generation (Resonanzueberbehoehung). Despite being far from the sensitivity, the sensitivity drops to a slight value that cannot be fully used. Coupled with the higher quality resonator frequency characteristics and naturally the transducer's long in-and-out vibration behavior, it makes accurate operating time measurement more difficult, thus reducing inaccuracy and low scan rate in flow-through measurement. Lead.

  Various attempts have been made to improve this situation. Attempts have been made to reduce the back echo in the piezoelectric transducer by a sound absorbing layer, so-called backing layer, and increase the bandwidth, for example, at a cost of sensitivity. A so-called impedance matching layer with respect to the wave resistance of the gas medium was also arranged with suitable results on the front face of the transducer. For example, since the piezoelectric rod is embedded in a synthetic resin polymer matrix, the transducer element itself is constructed as a composite, so that the wave resistance of this coupling element is lowered and at the same time an economical vibration mode is achieved. A signal analysis method was developed to achieve accurate operation time measurement despite long input / output vibration process. However, despite all the effort, the output capability of ultrasonic flow-through measurements remains limited by the narrow band nature of the sound transducers employed, particularly piezoelectric ultrasonic transducers.

  Another disadvantage of this transducer is its limited temperature stability. Piezoelectric materials with high piezoelectric sensitivity, such as commonly employed PZT-piezoceramics, lose their piezoelectric properties at the so-called Curie temperature with values ranging from approximately 250 ° C. to 350 ° C., depending on the material. And known piezoelectric materials with high temperature stability have almost perfect sensitivity for adoption as sound transducers.

  Conventional capacitive ultrasonic transducers do not have the desired temperature stability. A metal-coated diaphragm stretched over an electrically conductive substrate forms an insulating layer at the same time, and a synthetic resin or silicon nitride normally used as a dielectric diaphragm material cannot meet the temperature requirement for exhaust gas measurement. (DAHutchis, DWSchindel, AGBashford, and WMDWright, "Advances in Ultrasonic Electrostatic Conversion," Elsevier Ultrasonics, Vol. 36, 1998 "Non-Patent Document 3"). So-called electrical converters having a permanently polarized dielectric diaphragm, for example a Teflon polymer diaphragm with a stored charge carrier (electrons), do not have sufficient temperature stability.

  A particular disadvantage of conventional ultrasonic flowmeters with oblique radiation is the oblique position required in the normal transducer of the transducer relative to the tube wall. The resulting indentation or pocket causes an ultrasonic lead time that must be taken into account in the evaluation of the operating time. In addition, flow vortices are induced in the indentations and flows, which can cause measurement errors. In addition, vortices increase the problem of depositing particles that are transported with the flow. Particles deposited on the transducer diaphragm can greatly alter the propagation characteristics of the transducer. Known proposals for corrective measures, such as screens placed in the indentations, are permeable for ultrasound, impervious for flow, or cleaning the indentations with fresh air is problematic. It cannot be solved sufficiently.

  The use of a capacitive ultrasonic transducer does not provide any advantage. Improvements in the circuit are desirable with respect to eccentric voltages that substantially determine the electrical and mechanical operating points of the transducer. The required eccentric voltage, for example from 100 to 200 volts, is usually planned for the converter capacity via a high ohm electrical resistance. The resulting electrostatic force, on the one hand, results in a flat placement of the diaphragm foil on the structured back plate, and on the other hand, the linear transducer characteristics, i.e. the transducer sensitivity almost independent of the amplitude of the electrical transmission signal or acoustic reception signal. Play. However, the eccentric voltage prevents the preferred circuit concept in a normal piezoceramic or electrical converter, the simple use of an electric meter or charge multiplier directly related to the mass voltage.

  Both the charge amplifier and the electrometer amplifier are preferred and have approximately the same value for the SNR (English: signal to noise ratio, German: signal to noise ratio) achievable as a receiving amplifier. However, contrary to electrometer circuits, charge amplifiers allow higher bandwidths that should preferably be utilized with photodiodes or ultrasound, especially at high frequency uses such as optical data transmission. The high bandwidth stems from the fact that the eddy current capacities of the transducer and coupling cable are not transposed with the signal voltage in the charge amplifier concept. Since the operational amplifier generates a tentative voltage zero at the inverting input, the voltage associated with the converter and the parasitic components present remains as small as possible.

  However, due to the electrical eccentricity voltage required in capacitive ultrasonic transducers, charge amplifiers are not possible in the normal form. In a compromise solution, conventionally, an electric pressure transducer is connected by a charge amplifier operating with respect to mass voltage and a constant voltage coupling capacitor. However, it is no longer possible for pure charge amplifier operation of capacitive ultrasonic transducers to have all the advantages. The converter is no longer located directly at the virtual zero of the operational amplifier, which reduces the achievable bandwidth. A very large coupling capacitor overloads the converter, but for a converter with a marginal size, the total sensitivity of the converter + amplifier or its group operating time based on manufacturing condition variations of the converter capacity Is defined too small. In the case of ultrasonic flow-through measurement with operating time determination in two receiving channels, each asymmetry directly leads to a time error based on the group operating time, which should be evaluated as a very serious problem, so each The amplifier must be calibrated. The same applies to the coupling cable because the complex symmetry of both coupling cables in the final device configuration is difficult and expensive.

  As a possible surrogate for that, the electrical impedance transformation should be listed directly on the transducer in the housing. However, this should be removed due to lack of space and taking into account the high temperature of the combustion gas to be measured.

The above disadvantages of the prior art have particular significance in the measurement of exhaust gas flow in internal combustion engines, see in the exhaust gas train (see, for example, International Patent Application Publication No. 02/42730, “Patent Document 3” for PCT / AT01 / 00371) In particular, it prevents the realization of a preferred measurement technical device with a gas flow meter in a particularly intense and pulsating range. The individual use of motor-driven measurement techniques, such as measuring the blown gas (leakage gas from the crank housing of an internal combustion engine), for example, with a freely available gas flow meter is certainly covered, but in particular engine and drive train inspection. Possible applications of exhaust gas analysis on platforms and vehicle roller inspection tables or on vehicles on the road are narrowly limited.
European Patent Application No. 0797105 Specification German Patent Application No. 19636945 International Patent Application Publication No. 02/42730 KSMylvaganam, "Wide range ultrasonic gas flowmeter for monitoring sudden gas", IEEE treatment in ultrasonic, ferroelectricity and frequency control, 36, 144-149, 1989 IJO'Sullivian and WMDWright, "Ultrasonic measurement of gas flow using electrostatic transducers" Elsevier Ultrasonics, 40, 407-411, 2002 DAHutchis, DWSchindel, AGBashford, and WMDWright, "Advances in Ultrasonic Electrostatic Conversion," Elsevier Ultrasonics, Volume 36, 1998

  The object of the present invention is to provide an ultrasonic gas flowmeter with a substantially improved output, overcoming the difficulties described above, especially considering temperature stability and current temperature shape reduction and consideration. is there.

  Another object of the present invention is to improve an evaluation method for accurately and reliably detecting a gas volume flow or mass flow, particularly a high dynamic flow.

  This problem is implemented according to the present invention so that the sound transducer generates sound and receives a temporal transient sound signal as a positive displacement ultrasonic transducer, and the flow gas temperature shape is compared and standardized. This is solved by providing a device that minimizes the effect of temperature shape on the measurement.

  In order to obtain the high temperature stable embodiments required for many applications, according to the present invention, a metal diaphragm made of, for example, a titanium material, instead of the usual highly elastic and at least one-side metal-coated insulating diaphragm foil Is used.

  The through electrical conductivity of the diaphragm material naturally makes the construction of the positive displacement transducer more difficult. Instead of usually simply preparing an electrically conductive material for the second electrode of the capacitor forming the converter, special consideration must be given to the insulating layer. For this purpose, an electrode or a back plate with an insulating layer is used, which insulating layer preferably consists of a doped semiconductor and an insulating layer located thereon, which is coated, for example, with a diaphragm in particular. Place directly.

  In this case, it should be noted that the insulating layer corresponds to the basic material of the backing (semiconductor to be doped) with regard to its coefficient of thermal expansion. Therefore, it is particularly preferred when the insulating layer is formed by a material that occurs in the ambient atmosphere during the manufacturing process by the reaction of the material of the second electrode or backing plate under the action of heat. For example, a highly doped silicon base material can be treated in an oxygen atmosphere at approximately 1000 ° C. in a furnace for approximately 24 hours. In this case, a silicon oxide layer of approximately 1.5 μm is produced so as to satisfy the required insulation requirements. Layers grown out of this type of material relative to layers applied by sputtering or CVD techniques have a significant high thermal and mechanical loading capability.

  The frequency behavior, i.e. the sensitivity of the thus constructed high temperature ultrasonic transducer, is influenced by the resonant volume generated between the insulating layer and the diaphragm directly mounted thereon. For this purpose, the second electrode or the back plate is provided with a structure that can be used for the air effects that occur on the basis of the natural surface roughness.

  According to another embodiment, the second electrode or backing plate comprises a structure consisting of a discontinuous composite structure, in particular an etched structure. A linear or honeycomb structure with a characteristic width of 80 to 120 μm for a frequency range of attention from 100 to 600 kHz has proved to be particularly preferred. Furthermore, a direct dependency between the structural depth and sensitivity of the ultrasonic transducer occurs. With a structural depth of approximately 0.4 μm, particularly good results can be achieved for the required application. It should be noted that this structure can be manufactured in a green backing before manufacturing the insulating layer and after manufacturing the insulating layer. It is a semiconductor to be doped as well as an insulating layer. In this case, the large spacing between the electrodes charged between the unknitted area (the coupling element) and the diaphragm is adjusted, so that this configuration is more effective than when done after the manufacture of the insulation. The capacity is smaller. The production of relatively small structures is carried out according to the invention by the chemical etching method using the usual method of lithographic printing. That is, the entire back plate is first covered with a photosensitive rack (usually by a spinner) and then illuminated with the help of illumination marks in accordance with the rack manufacturer's manufacturing rules. Development of the rack in the developer bath opens the illuminated or unilluminated surface of the rack depending on the rack. Then the structure on the open surface in the etching bath can be etched deeply. At this time, the etching depth can be confirmed by the etching time.

  Preferably, the transducer has a plurality of separate mountable or decodable ranges in a linear or planar arrangement. Thereby, it is possible to remove the pouch holes in the transducer housing that can cause additional flow vortices in the area of the ultrasonic track. In particular, this so-called array transducer is manufactured by the above technique. The transducer has the advantage of allowing a characteristic oriented at an angle to the surface for sound emission or reception. As a result, it is possible to appropriately attach the wall of the ultrasonic transducer to the measurement tube even for the oblique passage sound of the tube. The individual ranges of the array transducer are mounted in a time discontinuous interval with the electrical transmission signal when used as a transmitter. When used as a receiver, individual received signals are evaluated with a time lag. In both modes of operation, the angular characteristics of the transducer can be influenced by variations in the time interval, thereby trying to prevent favorable drift phenomena as well as refraction phenomena.

The construction of this type of transducer is carried out analogously to the above process: for example high temperature stable materials (substrates) with insulating properties such as aluminum oxide (AL ₂ O ₃ ) or sapphire, for example platinum by sputtering or vapor deposition. A uniform structure of the electrode is produced. Thus, for example, for a flat and curved transmission or reception characteristic, the strip structure is applied to the substrate at 0.5 mm intervals from a 1 mm wide strip within a frequency range of approximately 100-600 kilohertz. In the second stage, an insulating layer is applied to the surface so that another attachment of individual electrode strips is possible by gluing. Then, the insulating layer is constituted by lithographic printing or etching technique as described above. On top of this structure, a metallic diaphragm rests in a conventional positive displacement ultrasonic transducer held by a transducer housing. With the adjustable emission angle realized by this type of transducer, the effects of sound refraction and sound drift can be prevented by temperature or flow shape.

  Another possibility precludes the above effect to configure the spacing between transmitter and receiver to be variable in the flow direction. This can be achieved, for example, by means of an embodiment according to the invention in which at least one sound transducer, in particular a receiving transducer, is movably supported. So, for example, with a tube diameter of 50 mm, it is moved exactly this distance at a flow rate of 30 m / s which produces a blowout downstream of approximately 10 mm, thereby ensuring the same propagation behavior as no flow.

  Efficiently, the rotatable bearings of one or more transducers can be adjusted to the maximum sound level even when the transmitter sound beam is at a higher flow rate or at a higher temperature difference between the tube wall and the flow gas. It leads that an appropriate action angle in sound emission can be intended to occur directly on the receiver surface. For this purpose, the transducer is mounted and mounted so that the input angle or output angle of sound emission can be changed with respect to the tube axis by rotation of the transducer.

  Furthermore, according to the invention, the high temperature difference between the tube wall and the flow gas is reduced or avoided by means of a heating device for the wall of the measuring tube as well as for the sound transducer. For this purpose, it is intended to adapt the tube temperature to the actual temperature of the flowing gas as much as possible by means of a known adjustment mechanism.

  For this purpose, in particular, the measuring tube is finished from a material with a small specific heat capacity, in particular from a thermally insulating material and / or provided with a coating from such a material and / or surrounded by a coating made of such a material. It is recommended to do. This means that, in the ideal case, the temperature of the measuring gas side wall always follows the gas temperature automatically and can be done without heating costs or at a slight heating cost.

  In addition, due to the high transient process in time, an installation that forms the temperature and / or flow shape is attached to the measuring rod so that the high transient process occurs during a load change, for example in the exhaust gas of an internal combustion engine, or It is preferable to integrate them. This leads to a comparative standardization of the temperature shape as well as the flow shape. According to the present invention, the tube bundle grids and portions are provided so that the tube bundle is used for flow lamination, while generally ensuring as uniform through-flow mixing of the turbulent flow and the resulting gas temperature. On the other hand, a uniform and swirling flow shape is obtained. In order to prevent separation of the temperature limit layer in the range of the bag hole provided in the converter housing, a grating that can be heated by a measuring tube without disturbing sound propagation is provided. Continue to close to the tube wall.

  In addition to pure mechanical measures that minimize the temperature profile of the flowing gas, it has been found to be particularly preferable to make additional calculation corrections on the results of the flow measurement depending on the additional physical parameters. Thus, it has been shown that changes caused by the temperature shape of the sound path are taken into account by additional correction factors in the evaluation of flow and sound speed calculations. In this case, it has been found that it is particularly preferable to change these correction factors depending on the tube temperature and the characteristic temperature of the gas. For this purpose, according to the present invention, a temperature sensor for measuring the temperature of the wall of the measuring tube is provided and connected to the evaluation electronic unit.

  Another embodiment of the device of the invention is provided with a separate temperature sensor for measuring the temperature of the flow and connected to the evaluation electronics.

  Furthermore, if an indication regarding the mass flow or the capacity flow defined as a constant temperature is generated as a measurement result, it indicates the dependence of the gas flow meter measurement results on the gas configuration that should not be neglected. Therefore, according to the present invention, a device for detecting the gas composition is provided, in particular a so-called lambda sonde for determining the air number λ. In particular, when measuring the exhaust gas mass flow on the inspection table, it has been found that a gas configuration depending on the number of air λ as a parameter is detected by a lambda sonde as a particularly preferable one.

  In doing so, gas composition considerations are made directly in the flow through evaluation (ie, independent of the original flow meter) and as provided by the invention, in the evaluation electronics of the flow meter itself. For this purpose, appropriate data lines and data interfaces are provided, which convey information about the gas configuration.

  For a correct and highly dynamic assessment of ultrasonic flow through, firstly, a primary signal that is as uninterrupted as possible with a large signal noise interval is required. To that end, it is responsible for the capacitive transducer and the analog primary processing of the signal. In order to avoid the above-mentioned problems regarding asymmetry and bandwidth in an amplifier circuit for a capacitive ultrasonic transducer, according to the invention, the receiving electronics are configured as an analog amplifier, and at least the reference potential of the primary amplifier stage is the potential of the transducer. The level is raised to the bias voltage. Thereby, commonly used coupling capacitors can be avoided, which significantly lowers the propagation bandwidth of the signal detection conversion amplifier, while capacitively loading the ultrasonic transducer. In this case, the connected capacitor means a capacitive load located in parallel with the converter in consideration of the actual zero point at the input of the amplifier circuit.

  In another particularly preferred embodiment, the inverting input of the amplifier circuit is directly connected to the capacitive converter.

  In order to protect the amplifier in the event of breakdown of the converter insulation, in the above embodiment the capacitive converter and the reference potential are connected via a capacitor to the inverting input of the amplifier circuit, but this implementation The embodiment acts as a pure protection rather than as a normal coupling capacitor, because the same voltage, ie the bias voltage, abuts on both sides of this capacitance. The magnitude of this capacitance can be chosen very large in this case, for example 100 nF, because in this case the converter is loaded by a series circuit of the internal resistance and capacitance of the bias voltage source. is there. However, the internal resistance is so high that the load on the transducer can be neglected in the standard case.

  The capacitance of the capacitive ultrasonic transducer means an RC-element and a low-pass filter with respect to a bias voltage failure due to a bias voltage coupling resistance. Since the same voltage, that is, the bias voltage is in contact with the non-inverting input of the amplifier (in some circumstances, it is separated from the converter potential by the capacitor), the reference potential is similarly applied to the RC-element at the non-inverting input of the amplifier circuit. It is preferable to suppress a failure in the non-inverting input portion of the amplifier by contacting with each other, and this invention is provided.

  Preferably, the special embodiment is provided that the time constant of this RC-element is approximately the same as the time constant of the filter formed from the converter capacitance of the reference potential and the coupling resistance.

  In order to suppress the disturbing signal rate outside the frequency range used, for example 300-400 kHz, another filter of the invention is connected back to the primary amplifier circuit, in particular the high-pass filter in the next band A second amplifier stage comprising a pass filter and possibly at least one isolation capacitor is connected backwards. In this case, the separation of the utilization signal from the bias voltage is optionally performed before, during and after this circuit by a voltage stable coupling capacitor.

  According to the present invention, an apparatus for measuring an exhaust gas flow from an internal combustion engine is characterized in that a gas flow meter according to one of the above paragraphs is installed in an exhaust gas column of the internal combustion engine. Due to the pulsating and very hot exhaust gases in many driving conditions, an accurate and highly dynamic measurement of the flow-through is carried out so that it rests in the vehicle on the examination table or in the workplace or in vehicles in normal operation. Direct use of the individual cylinders in the outlet chamber can be considered as well as before and after the catalyst installation and between the sound attenuator and the end of the exhaust gas train.

  According to a preferred embodiment, it is further intended that the gas flow meter is provided in the immediate vicinity of where gas removal may occur, which determines harmful material components in the exhaust gas.

  Of course, if a measurement is required and / or the installation location is more convenient, the gas flow meter can be installed in a conduit section that is flowed by a partial flow of exhaust gas of the internal combustion engine.

  In order to obtain as complete a state of the internal combustion engine as possible, all gas flows are monitored in the most convenient case, and for that purpose preferably a gas flow meter is passed through by the gas flow diluting the exhaust gas of the internal combustion engine It can be intended to be installed in a part.

  In order to improve the initially described evaluation method, rather than just improving the gas flow-through measurement with capacitive sound transducers from an instrumental point of view, according to the invention, the flow-through assumption is determined after the operating time has been determined. It is intended to be evaluated and corrected at least by the characteristic temperature of the gas and the temperature of the tube wall.

Considering the constant k ₁ which depends on the flow shape, the two constants k ₂ and k ₃ which depend on the operating time in the flow direction t ₊ , the operating time with respect to the flow direction t _{= and the} pipe geometry are first the flow velocity v Is estimated and the speed of sound c is determined:

容積貫流Ｖ＆の第一仮定値を測定管の横断面積Ａによる掛算によって方程式ＥＱ１から求める：

A first hypothetical value for the volumetric flow-through V & is obtained from equation EQ1 by multiplication by the cross-sectional area A of the measuring tube:

この仮定値は特徴的温度Ｔ_C 並びに管壁の温度Ｔ_W に依存して関数ｆ₁ （Ｔ_C ，Ｔ_W ）によって訂正される：

This assumption is corrected by the function f ₁ (T _C , T _W ) depending on the characteristic temperature T _{C and the} tube wall temperature T _W :

現実の質量流の値に関して興味があるならば、これは公称密度による掛算によって方程式ＥＱ４から算出され得る。

If interested in actual mass flow values, this can be calculated from equation EQ4 by multiplication by nominal density.

In addition, in another refined embodiment of the method, it is intended that the actual pressure value in the measuring tube is taken into account particularly precisely at the point of operation time measurement in order to determine this hypothetical value. Yes. Thereby a sudden density change of the flow medium can be influenced in the calculation.
For this purpose, the actual density ρ is determined from the sound speed c (EQ2) calculated from the operating time, the special heat capacity k and the actual pressure p:

In another special embodiment, the assumed value is corrected depending on the temperature coefficient of the characteristic temperature of the gas and the temperature of the wall of the measuring tube.
Thus, the functional relationship of the function f ₁ (T _C , T _W ) in the equation proved to be particularly favorable:

その際にｋ₄ は経験的に或いは理論的仮定に基づいて流れ形状と温度形状によって求められる定数である。

In this case, k ₄ is a constant determined by the flow shape and the temperature shape empirically or based on theoretical assumptions.

  In order to determine the temperature mentioned in this case, according to the invention it can be intended that the temperature of the tube wall or the temperature of the gas in the measuring tube or both temperatures are also measured. For this purpose, a customary temperature sensor can be installed.

  In this case, of course, there is a disadvantage that the temperature sensor has a slow reaction time particularly in the measurement of gas temperature, and the reaction time can be changed to, for example, a few milliseconds in a very short time interval. Therefore, according to the present invention, it is intended that the characteristic temperature of the gas is detected based on a physical model of the temperature shape in the measuring tube from the operating time and the assumed value of sound velocity.

Furthermore, according to the invention, it is intended to further clarify the characteristic temperature of the gas in view of the temperature of the wall of the measuring tube.
The speed of sound c detected by measuring the operating time means the average value of the speed of sound c to (r) (r is the radius of the radially symmetric tube and R is the radius of the tube) depending on the location across the tube cross section:

さらに、局部的音速の次の表示形態の理想的ガス等式に一致して求められる：

Furthermore, it is determined in accordance with the ideal gas equation of the following display form of local sound velocity:

この場合にｆ₂ (r) は温度形状の形状を示し、Ｍはガスのモル質量を示し、Ｒは理想的ガス定数を示す。
方程式ＥＱ７とＥＱ８からガスの特徴的温度が求められ得る。

In this case, f ₂ (r) indicates the shape of the temperature shape, M indicates the molar mass of the gas, and R indicates the ideal gas constant.
The characteristic temperature of the gas can be determined from equations EQ7 and EQ8.

  As already mentioned, the temperature change in the gas takes place very quickly so that the temperature measurement can be performed so that the temperature measurement and the operating time measurement are valid for the same volume. preferable. It can be achieved by taking into account the geometry of the arrangement and the flow rate in the selection of the time points for temperature measurement and operating time measurement.

  In a special embodiment of this method, in calculating the assumed value of the flowing gas volume, the adiabatic coefficient k, i.e. the nominal value of the ratio of the special heat capacity at constant pressure and volume, is employed for the calculation of the gas volume. It is intended to take into account the gas composition of the medium.

Furthermore, it is intended to correct this nominal value in accordance with the characteristic temperature of the gas, ie a temperature-dependent adiabatic coefficient k (T _C ) is adopted in equations EQ8 and EQ5 in accordance with the gas composition. ing.

  In order to accurately detect the ultrasonic operation time in consideration of the parasitic reflection signal, according to the present invention, the expected time window is obtained depending on the transmission time of the ultrasonic signal and the assumed value of the operation time. A search is then performed after the correct arrival time of the received signal in this time window.

  Furthermore, it is intended to be adapted depending on the series at the time of transmission, i.e. the operating time at which the measurement repetition rate is estimated, so that the parasitic reflection signal within the expected time window is predicted before the original utilization signal. It can be achieved that it is not located.

  The operating time of the measurement can be taken into account according to the first method embodiment in a simple form as an assumed value of the operating time.

  Other method aspects with great accuracy, although at a low cost for detection, are intended to take into account the calculated values modeled as a hypothetical value depending on the results of the flow-through measurement. Has been.

  In another preferred embodiment of this method, the calculation time for the start of the received signal is first confirmed in order to determine the operating time, and by analyzing the phase information of the received signal, the exact start is illustrated in a complex value. It is intended to be confirmed.

  In order to obtain a complex value of the received signal, for example, the Hilbert transform of an ideal received signal can be used.

  In a particularly preferred embodiment of the method for evaluating the actual received signal, the actual phase position of the display of complex values of the received signal is determined and calculated at the start of the received signal at any point in the range of continuous change. The phase position is confirmed.

  Preferably, the time of occurrence of the maximum amplitude can then be taken into account for the calculation time of the start of the received signal. With this type of method, the arrival time can be ascertained with at least uncertainty in the half-period (± T / 2) of the transmitted signal.

In order to improve the accuracy, further, starting from the calculation time of the start of the received signal, the exact start of the received signal can be determined based on the phase position initially caused.
In particular, the first zero passage of the received signal is defined as the arrival time of a certain sound characteristic.

The invention will now be described on the basis of some exemplifications of preferred embodiments of the invention:
In this case, FIG. 1 schematically shows the gas flow meter of the present invention, FIGS. 2 and 2a show an overall view and a detailed view of the capacitive ultrasonic transducer of the present invention, and FIG. FIG. 4 schematically shows an amplifier circuit of the present invention for a primary signal of a capacitive ultrasonic transducer, FIG. 5 is a display of the evaluation method in block diagram form, and FIG. Indicates the transmission and reception signal display of the transmitter and receiver pair and the associated phase signal of the reception signal.

  The vertical cross-sectional display of the gas flowmeter device of the present invention in FIG. 1 shows a measuring tube, and gas flows through the measuring tube, and the volume and mass of the gas are obtained. The measuring tube 1 has a heating element 2, with the help of that element the temperature of the measuring tube 1 can be controlled via the evaluation electronics 3 and heated by the intermediate circuit of the heating control electronics 4. The measuring tube 1 is preferably additionally provided with a flow shape and temperature shape forming installation 5 at least before the operating time measurement point (in relation to the main flow direction of the tube). This mounting part 5 can be formed as a bundle of tubes or guide lamina having a slightly smaller diameter than the measuring tube 1.

  Transmitting transducers 7 and 8 and receiving transducers 9 and 10 at a pocket or tube connection of the measuring tube 1 which can be closed by a cover 6 which is sound permeable and closes the walls of the measuring tube 1 in bundles, for example. Are assembled to form a capacitive ultrasonic transducer. The capacitive transducer 7-10 and the cover 6 can be heated via the heating element 2 for the wall of the measuring tube 1 or via a separate separate heating element.

  The ultrasonic transducer 7-10 is supported by an insertion part which is movable in the longitudinal direction of the measuring tube 1 in all cases, in particular only the reception transducers 9 and 10, which insertion part can be adjusted, for example, by a spindle with a step motor. . The movement can then be carried out under the control of the evaluation electronics 3 adapted to the driving. The longitudinal adjustment of the transducer 7-10 is performed in a predefined discontinuous process.

  However, the transducers 7-10 can be mounted so as to be able to rotate in or near the measuring tube 1 and are preferably arranged in parallel to the longitudinal axis of the measuring tube 1 and parallel to the tangent to the wall of the measuring tube 1, respectively. It can be supported so as to be rotatable about an axis oriented at 7-10 installation points. This kind of arrangement also tries to prevent the drift phenomenon of the sound signal, and the refraction effect can also be considered.

  Further, FIG. 1 schematically shows a reception electronic unit 11, which performs amplification and primary analog processing of a reception signal. The receiving electronic part is connected to an evaluation electronic part 3 that controls the control electronic part 4 for generating and heating the transmission signal. As an additional input signal, the evaluation electronics 3 is made to use the result of at least one temperature sensor 12 for gas temperature and one temperature sensor 13 for wall temperature and preferably the value of one pressure sensor 14. Similarly, in order to consider all cases of gas configurations suitable for gas flow calculation, there may preferably be one lambda sonde 15 which evaluates the actual air number information via the transmission line. Transfer to part 3. As an alternative for this, information about the gas configuration can be transferred from the exhaust gas analyzer to the evaluation electronics 3 via a data transmission line 16 (illustrated by a dotted line).

  FIG. 2 shows the capacitive ultrasonic transducer of the present invention employed in the gas flow meter apparatus of FIG. 1, and FIG. 2a is a detailed enlarged portion of the front end of the ultrasonic transducer, through which the sound signal is gas. To be introduced. The transducer main body 17 is provided with a metallic diaphragm 18 as one electrode and a back plate 19 as a second electrode of an actual operating member of the sound transducer. In the detailed view of FIG. 2a, the configuration of the back plate 19 can be recognized as a regular ridge 20 shape, which is preferably etched into the insulating layer 21 of the back plate 19, so that both electrodes, A fixed distance is guaranteed between the diaphragm 18 and the doped back plate 19.

  In the case of FIG. 2 a, the structure 20 was formed after the insulating layer 21 was manufactured. At that time, the back plate 19 is first oxidized, and then the structure is formed in the insulating layer 21 by etching. However, first, the structure 20 of the back plate 19 is formed, and then the insulating layer 21 is manufactured. For this purpose, the carrier material is first etched and then oxidized.

  FIG. 3 is a cross-sectional view showing a schematic configuration of the capacitive array converter of the present invention. In the same manner as in FIGS. 2 and 2a, the transducer body 22 is provided with a metallic diaphragm 23 and a back plate 24 as first and second electrodes. In this case, the back plate 24 is composed of a base of an insulating base material 25, an electrode 26 and an insulating layer 27 that can be individually contacted and can be individually attached to the base. The substrate 25 on which the electrodes are deposited or sputtered, for example, can consist of ceramic, sapphire or nitric oxide, for example.

  The high temperature stable array transducer has substantially two advantages, as illustrated in FIG. First, the pockets or indentations in the measuring rod 1 are no longer necessary due to the appropriate installation of the inner wall of the rod, and secondly the direction of the sound bundle for the transmission or reception operation is simply determined by the appropriate electronics in the individual transducer area. It is adjusted during operation by control and readjusted appropriately to take into account the drift of sound emission into the gas stream.

  FIG. 4 schematically shows the structure of a receiving amplifier which is integrated in or connected to the evaluation electronics 3 in particular. In the figure, an auxiliary circuit diagram 28 of the capacitive receiving ultrasonic transducer 9 or 10 is shown with a dotted line. A bias voltage VB is connected via a coupling resistor 29. A converter is connected to the next amplifier 30 via a capacitor 31, which is used, for example, to protect the amplifier circuit in case of breakdown of the converter insulator. Similarly, a bias voltage VB is connected to the amplifier 30 at the input that is not reversed via the RC-member 32. In order to create a symmetrical relationship at the input of the operational amplifier 30, the time constant of the RC-element 32 is preferably about the same as each of the connected ultrasonic transducers, ie the resistance of the RC-element 32 is The capacitance of the RC-element 32 matches the capacitance of the converter 9 or 10 with the bias resistance at the reversed input. This provides the advantage that the non-inverting input of the operational amplifier 30 due to approximately the same critical frequency results in a faulty low-pass filter present in the same voltage in some circumstances, as well as a bias resistor for the inverting input. This is the case with the capacitive converter itself.

  The amplifier 30 is supplied symmetrically around the bias voltage potential. The reception signal of the reception ultrasonic transducer 9 or 10 is supplied to another processing section via one separate coupling capacitor 33 and a preferably interconnected filter circuit 34 which is no longer at the bias voltage potential. In order to achieve the necessary total amplification (up to 80 dB), a second amplifier can be connected, especially under the filter circuit 34. To that end, an electronic meter multiplier is provided. Adjustment of the total amplification (AGC, automatic gain control) of the reception electronics is performed in this second stage according to the purpose. The change in amplification in the first stage can thus be strongly influenced by frequency propagation behavior.

  FIG. 5 schematically shows the evaluation method according to the invention in block representation; in the first stage 35, the flow velocity v at the operating time of the ultrasonic wave in the direction opposite to the gas flow direction to be measured from the input values t + and t- Assumed values of 'and sound speed c' are calculated according to the usual formula. The values of flow velocity v and sound velocity c in the second stage 36 taking into account the geometric values encoded by the input value {L} and / or the wall temperature TW of the measuring tube 1 and / or the characteristic temperature TG of the gas. Improved calculations are required. Due to the simple but not the only model of conditions in the measuring tube 1, the correction of the flow through assumption is made by a linear correction factor of the flow velocity, which is the simplest model and is linear with the characteristic temperature of the gas. Depends on the nominal temperature difference from the temperature of the measuring tube wall.

  In order to show that the characteristic temperature of the gas can be determined not only by measurement, but also from the speed of sound in consideration of the amount of material, a substitute calculation process 36a is shown in dotted lines. In the final stage 37, the input value κ (kappa), the adiabatic coefficient, the gas characteristic temperature, the air number λ (lambda), and the gas mass M flowing or the gas volume V flowing depending on the actual pressure p are sometimes obtained depending on circumstances.

  In the detection of gas flow from the sound transient time, an acceptable control is preferably intended with respect to the theoretical mean sound velocity in the measuring tube 1. A known relationship between the gas temperature TG and the speed of sound c results from the molar mass of the gas, the universal gas constant and the temperature-dependent adiabatic coefficient of the gas, which speed of sound can be used for acceptability testing. In order to detect the value of the molar mass, the gas relationship is determined, for example, by the lambda sonde 12 or other analyzer. This is further required for the calculation of the temperature-dependent adiabatic coefficient κ (T), and the dependence of the temperature T cannot be ignored especially when detecting the flowing gas mass M or flowing gas volume V.

  Next, the accurate detection of the present invention at the time of arrival of the ultrasonic signal will be described with reference to FIG. In this case, three signals are shown in FIG. 6 along the same time axis. At the top, the transmission signal S existing in the shape of a brush having three wavelength characteristics is recognized. The actual received signal is shown in the center of FIG. A utilization signal 38 as well as a parasitic reflection signal 39 can be recognized, and this utilization signal is generated at the receiver by direct reception of sound pulses emitted from the transmitter, and this reflection signal 39 is transmitted to the transmitters 7 and 8 and the receiver 9. Based on several times the reflection between 10. They arrive at the receiver after an odd number of passes several times in the transmitter / receiver interval depending on the effective sound speed of the medium. Therefore, the parasitic reflection signal shown in the figure is derived from the transmitted pulse preceding the transmitted pulse (brush) shown in the display.

  The lowest signal φE indicates the phase position of the received signal illustrated in a complicated manner through, for example, Hilbert transform or similar renormalization integration. In the region where the actual use signal exists in the same manner as the parasitic reflection, it is possible to recognize the continuous change of the phase position. Upon arrival of the pulse at the transducer, the phase begins to rotate with a relatively uniform gradient. This gradient depends on the signal frequency of the received signal. At the first displacement of the received signal E, the phase no longer rotates completely over the full amplitude because the first displacement forms a transition from phase noise to pulse. Where the displacement has a maximum value, the phase intersects the zero line. The phase noise should be observed before the pulse arrives.

  From the first assumed value t1 of the operating time of the ultrasonic signal, an expected time window T ± is defined around this assumed value t1. Within this time window, an improved hypothesized value of the operating time tL is searched. For this purpose, the maximum amplitude value of the reception signal E is obtained as an improved assumed value t2. From this value, each time point t3 is obtained in the direction of the transmission time point, and the continuous change of the phase position ends at this time point. From this new assumed value t3, a time point t4 is obtained in the positive time direction, and at this time point, the first zero passage of the received signal is obtained. This point in time, which is shifted to the actual arrival point of the received signal for half a period, is corrected computationally and taken into account as the operating time for further processing.

  As described above, the received signal is composed of an overlap of the utilization signal and the parasitic reflection signal. The time interval between the received signals associated therewith is between signals originating from the same transmission pulse and is an even multiple of the average operating time in the flow direction and opposite to that direction. However, this average operating time is mainly determined by the actual sound speed of the medium, and is thus determined over a wide range from the actual temperature.

  For many application ranges, the temperature of the gas can be dropped quickly over a wide range. This inevitably causes severe problems, since the reflected signal is very similar to the actual received signal in terms of characteristics such as signal shape and phase, making it difficult to evaluate accurately in time and leading to error measurements. Interference overlap between the utilization signal and the reflected signal occurs in the range of the expected time window to be obtained.

  Since the solution proposed by this invention of this problem is to influence the measurement repetition rate, an overlap between the received signal E and the first or second reflection can be avoided. The optimum measurement repetition rate can be calculated according to the assumed value of sound velocity, where the first reflection and the resulting second reflection are always present after the actual received signal with a freely selectable time safety interval. Since this safe period is selected as short as possible, a high measurement repetition rate is possible, and the previous range of the received signal is kept “clean” with respect to another reflection from the second. Furthermore, it is meaningful to create this safety interval depending on the period of the transmission signal.

  Preferably, the received signals overlap each other as long as there is a sufficient time interval for the received signal E and the next received signal E due to the first both reflections. Thereby, the measurement repetition rate can be increased as required.

  If the measurement repetition rate is to be adjusted appropriately, an appropriate time mark must be stored with the calculated mass flow value and the mass flow history can be reconstructed over time.

1 schematically shows a gas flow meter of the present invention. The whole figure and detailed drawing of the capacity type ultrasonic transducer of this invention are shown. The capacitive ultrasonic transducer is shown in an array configuration. 1 schematically shows an amplifier circuit of the invention for the primary signal of a capacitive ultrasonic transducer. It is a display of the evaluation method in a block diagram form. The transmission and reception signal display of the transmitter and receiver pair and the associated phase signal of the reception signal are shown.

Explanation of symbols

1. . . . . Measuring tube . . . . 2. heating element . . . . Evaluation electronics section 4. . . . . 4. Heating control electronics . . . . Installation section 6. . . . . Cover 7-10. . . Converter 11. . . . Receiving electronic unit 12,13. . . Temperature sensor 14. . . . pressure sensor
15. . . . Lambdasonde 16. . . . Data transmission line 17. . . . Converter body 18. . . . Metal diaphragm 19. . . . Back plate 20. . . . Configuration 21. . . . Insulating layer 22. . . . Converter body 23. . . . Metallic diaphragm 23
24. . . . Back plate 25. . . . Insulating base material substrate 26. . . . Electrode 27. . . . Insulating layer 28. . . . Auxiliary circuit diagram 29. . . . Coupling resistance 30. . . . Amplifier 31. . . . Capacitor 32. . . . RC-element 33. . . . Coupling capacitor 34. . . . Filter circuit 35, 36, 37. . . Step

Claims (46)

  In an ultrasonic gas flowmeter based on an operating time method comprising a gas flow-through measuring tube, at least one transmission sound converter, one reception sound converter, and transmission reception evaluation electronics, a sound converter (7, 8, 9 , 10) is a capacitive electro-acoustic ultrasonic transducer designed to generate and receive temporally transient sound signals, comparatively adjust the flow gas temperature shape and minimize the influence of the temperature shape on the flow measurement An ultrasonic gas flowmeter is provided.   Gas flow meter according to claim 1, characterized in that the converter (7, 8, 9, 10) comprises a metal diaphragm (18, 23), for example made of titanium material.   The back plate (19, 24) is composed of a doped semiconductor and an insulating layer (21, 27) overlaid thereon, and the diaphragm (18) is particularly directly placed at a location where the insulating layer is applied, for example. The gas flowmeter according to claim 2, wherein:   Insulating layer (21, 27) is formed by a material generated under the action of heat by the ambient atmosphere during the manufacturing process by reaction of the material of the second electrode, ie the back plate (19, 24). 3. The gas flow meter according to 3.   Gas flow meter according to claim 3 or 4, characterized in that the second electrode, i.e. the back plate (19, 24) comprises one configuration (20).   6. Gas flow meter according to claim 5, characterized in that the second electrode with one configuration (20), i.e. the back plate (19, 24), has a discontinuous synthetic structure, preferably a corroded configuration. .   7. The transducer (7, 8, 9, 10) has a plurality of separately mountable regions (26) in a linear or planar arrangement. The gas flowmeter described in 1.   8. The at least one sound transducer (7, 8, 9, 10), in particular the receiving transducer (9, 10), is movably supported. The gas flowmeter described in 1.   The gas flowmeter according to any one of claims 1 to 8, wherein one or a plurality of sound transducers (7, 8, 9, 10) are rotatably supported.   10. The heating device (2) for the wall of the measuring tube (1) is also provided in the sound converter (7, 8, 9, 10) as the case may be, according to any one of the preceding claims. The gas flowmeter described in 1.   The measuring tube (1) is manufactured from a material with a small specific heat capacity, in particular a heat insulating material and / or provided with a coating of this kind of material and / or surrounded by a coating of this kind of material The gas flow meter according to any one of claims 1 to 10, wherein the gas flow meter is provided.   12. The mounting part (5, 6) forming the temperature and / or the flow shape is installed in or integrated with the measuring tube (1). The gas flowmeter according to item.   13. At least one temperature sensor (13) is provided for measuring the temperature of the wall of the measuring tube (1) and is connected to the evaluation electronics (3). The gas flowmeter according to any one of the above.   14. At least one temperature sensor (12) is provided for measuring the temperature of the flow and is connected to the evaluation electronics (3). Gas flow meter.   15. A gas flow meter according to claim 1, wherein a device for detecting the gas composition, in particular a lambda sonde (15), is provided.   16. A gas flowmeter according to any one of the preceding claims, characterized in that a data lead (16) and a data interface are provided, through which information about the gas composition of the flow is communicated.   The receiving electronics (11) is configured as an analog amplifier, and at least the reference potential of the primary amplifier stage (30) is raised to the potential level of the converter (9, 10), ie the bias voltage. The gas flowmeter according to any one of claims 1 to 16.   18. A gas flow meter according to claim 17, wherein the inverting input of the amplifier circuit (30) is directly connected to the capacitive converter (9, 10).   19. Gas according to claim 17 or 18, characterized in that the capacitive converter (9, 10) and the reference potential are connected to the inverting input of the amplifier circuit (30) via a capacitor (31). Flowmeter.   20. The non-inverting input part of the amplifier circuit (30) is similarly in contact with a reference potential via an RC-element (32), as claimed in any one of claims 17 to 19. Gas flow meter.   21. Gas flow rate according to claim 20, characterized in that the time constant of the RC element (32) is approximately the same as the time constant of the filter formed from the converter capacitance and the reference resistance coupling resistor (31). Total.   The primary amplification stage (30) is connected after another filter (34), in particular the high-pass filter, in some cases the second amplification stage is connected after the next bandpass filter and possibly at least one isolation capacitor. The gas flow meter according to any one of claims 17 to 21, wherein the gas flow meter is provided.   An apparatus for measuring an exhaust gas flow of an internal combustion engine, wherein the gas flow meter according to any one of claims 1 to 22 is installed in an exhaust gas train of the internal combustion engine.   24. The apparatus according to claim 23, wherein the gas flow meter is provided in the immediate vicinity of a portion having no resistance of the gas extraction portion that determines the harmful substance component in the exhaust gas.   25. An apparatus according to claim 23 or claim 24, wherein the gas flow meter is inserted into a conduit portion that is flowed by a partial flow of exhaust gas of the internal combustion engine.   25. An apparatus according to claim 23 or claim 24, wherein the gas flow meter is inserted into a conduit portion that is flowed by a gas flow that dilutes the exhaust gas of the internal combustion engine.   In the method of detecting the gas flow rate detected by the two sound signals between the transmitter and the receiver having an average flow velocity and the amount of gas flowing from the operating time with high temporal resolution, the flow rate is determined after the operating time is determined. The assumption is evaluated (35), which is corrected by at least the characteristic temperature of the gas and the temperature of the wall of the measuring tube (36).   28. The method according to claim 27, characterized in that, in order to determine the assumed value of the flow rate, it is related to the actual pressure value of the measuring tube, in particular precisely to the location of the operational measurement.   29. A method according to claim 27 or claim 28, wherein the assumed value is modified depending on the characteristic temperature of the gas and the temperature of the wall of the measuring tube.   30. A method according to any one of claims 27 to 29, wherein the temperature of the wall of the measuring tube is measured.   The method according to any one of claims 27 to 30, wherein the temperature of the gas in the measuring tube is measured.   32. The gas characteristic temperature is detected from an operating time and a hypothetical value for sound speed based on a physical model of a temperature shape in the measuring tube, thereby detecting the characteristic temperature of the gas. The method according to item.   The method according to claim 32, wherein the characteristic temperature of the gas is accurately expressed by considering the temperature of the wall of the measuring tube.   34. A method according to claim 27 or claim 33, wherein the geometry of the device and the flow rate are taken into account when selecting the time points for temperature measurement and operating time measurement.   35. The nominal value of the adiabatic coefficient for calculating the gas quantity is taken into account in order to take into account the gas composition when correcting the assumed value of the gas quantity (37). The method according to claim 1.   36. The method according to claim 35, wherein the nominal value of the adiabatic coefficient is modified in accordance with the characteristic temperature of the gas.   37. The expected time window for the arrival time of the received signal is determined depending on the transmission time of the ultrasonic signal and the assumed value of the operation time. the method of.   38. A method according to any one of claims 27 to 37, wherein the continuity at the time of transmission, i.e. the measurement repetition rate, is adapted depending on the assumed operating time.   39. A method according to claim 37 or claim 38, characterized in that an operating time of a previously measured measurement is used as an assumed value of operating time.   39. A method according to claim 37 or 38, characterized in that a calculated value modeled in dependence on the result of a flow measurement performed in advance is used as the assumed value of the operating time.   In order to determine the operating time, first a hypothetical time point for the start of the received signal is first confirmed, and the precise start is confirmed by analysis of the phase information of the received signal illustrated in a complex value. 41. A method according to any one of claims 37 to 40.   42. The method of claim 41, wherein the complex received signal is determined by a Hilbert transform of the actual received signal.   The actual phase position of the complex representation of the received signal is determined for the actual received signal, and the assumed time point for the start of the received signal is confirmed at any point in the region of continuous change of the phase position. 42. The method of claim 41.   42. The method according to claim 41, wherein a point of occurrence of maximum amplitude is used for a hypothetical point in time of the start of the received signal.   42. The method according to claim 41, characterized in that starting from a hypothetical point in time for the start of the received signal, the precise start of the received signal is determined based on the initial phase position.   The method of claim 45, wherein the first zero pass of the received signal is defined as the arrival time of the desired signal feature.

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